1. Field of the Invention
This invention relates to support appliances and is particularly, although not exclusively applicable to mattresses, pillows and the like.
2. Description of the Prior Art
My U.S. Pat. No. 3,822,425 discloses an air support appliance, for example, an air mattress which comprises an envelope of material which is inflated by air under pressure flowing continuously through the mattress. The surface material of at least the upper surface of the mattress is a material which is substantially impermeable to liquids and solids but is capable of transmitting water vapour when the water vapour partial pressure is higher on one side of the material than the other so that water vapour generated by the user of the bed passes through the upper surface of the mattress and is carried away with the continuous stream of air flowing through the mattress. A disadvantage with the air mattress described above is that air pressure is required not only to purge the mattress but also to support the user of the bed and this requires a substantial air pump. It is an object therefore of this invention to provide a construction of support appliance on which there is less dependence on air pressure for supporting the user of the appliance.
My U.S. Pat. No. 3,949,438 discloses a support appliance in the form of a mattress of a resilient foam material having interconnecting air transmitting cells and an upper surface which has at least an impedance to gas flow whilst permitting transmission of water vapour from the outer to the inner side thereof for removal by air flow through the mattress effected by an air pump. Here again it has been found that a substantial air pump with an elaborate system for controlling air temperature must be provided to ensure air flow through the mattress and to ensure that undue heating or cooling of the mattress which would cause discomfort to the user does not occur.